Radiation resistant fluids



United States Patent 3,351,553 RADIATION RESISTANT FLUIDS Ralph Hollinghurst, Thundersley, Essex, England, assignor, by mesne assignments, to Mobil Oil Corporation, a corporation of New York No Drawing. Filed July 9, 1963, fler. No. 293,803 Claims. (Cl. 252-45) The present invention relates to fluids suitable for a variety of purposes and having the property of resistance to the effects of nuclear radiation and being also thermally stable. The invention more particularly relates to fluids suitable for use in applications Where petroleum oil products would normally be used but for their susceptibility to the effects of radiation.

Radiation resistant fluids'are' known containing, for instance, fused aromatic'ring compounds or alkyl derivatives of such compounds. Such fluids are used for example as coolants and moderators for nuclear reactors, and in lubricating oil; possibly accompanied by inhibitors, such as aromatic selenides. Polyphenyls show a good thermal stability and resistance to degradation by exposure to radiation but they have a melting point which limits their usefulness in lower temperature regions, and they have a relatively low boiling point. Known polyphenyls are thus not satisfactory at temperatures such as 100 F. p 5 j It is an object'of the present invention to provide a radiation resistant fluid and it is also an object of the invention to provide such a fluid which is thermally stable. It is a further object of the invention to provide a radiation resistant fluid satisfactory for use at temperatures lower than "hitherto applied. Further objects include the; provision of such fluids as coolants and/or moderators in nuclear reactors, lubricants, hydraulic fluids and heat transfer media generally, for use in circumstances involving exposure to nuclear radiation.

The invention is based on the observation'that partially hydrogenated terphenyls which are fluids at ambient temconsisting of or containing a partially hydrogenated polyphenyl, such as a partially hydrogenated terphenyl. The invention further embraces apparatus exposed to nuclear radiation and containing a fluid comprisingat least one partially hydrogenated polyphenyl, such as a partially hydrogenated terphenyl.

Partially hydrogenated terphenyl mixtures particularly suitable for inclusion in fluids according to the present invention are those obtained by the 'partial hydrogenation'ofa by-pr'oduct hydrocarbon fraction formed in the manufacture of biphenyl by the pyrolysis of benzene. These partially hydrogenated terphenyls or mixed partially hydrogenated terphenyls and the manner of preparation thereof are fully disclosed in US. Patent No.

2,364,719, wherein they are referred to as partially hydrogenated hydrocarbon liquid mixtures. A typical material', employed in the various examples and tests presented herein, has the following physical characteristics:

Composition L Partially hydrogenated terphenyls.

"Appearance Colorless, oily liquid.

Viscosity, SUS

At 100 F 124-164. At 210 F 38-40. Pour Point, C 26 to -28. Distillation Range First Drop C 340-349. 10% C 345-358. 50% C 353-360. 90% C 362-389. 95% C 371-396.

This particular material is marketed by Monsanto Chemical Company of St. Louis, Missouri, under the Tradename HE-40. See Monsanto Technical Bulletin No. PL-40, June 1961.

According to a further feature of the invention, a fluid for use according to the invention may also contain a proportion of a polyphenyl, such as diphenyl, or a solid polyphenyl or alkyl derivative thereof. A preferred radiation resistant fluid may comprise, for instance, a mixture of (a) a partially hydrogenated terphenyl with (b) from about 1% to about 30%, by weight, of diphenyl. It is also contemplated, according to the invention, to incorporate along with the partially hydrogenated terphenyl from about 1% to about 30%, by weight, of a polystyrene or an alkyl derivative thereof, such polystyrene or alkylated polystyrene having a molecular weight of about 5,000 to about 100,000 and preferably fromvabout 10,000 to about 50,000.

Fluids according to the invention may also co'nfain free radical inhibitors, such as alkyl or aryl selenides, or aryl disulfides, such asdiphenyl disulfide and dibenzyl disulfide, in amounts of from about 1% to about 10%, by Weight of the total composition. The fluids of the invention may be blended with petroleum oils, kerosine and the likes Thus, hydraulic fluids, bearing lubricants, gear lubricants and the like may be formulated according to physical characteristics required for use where radiation makes a normal petroleum oil unsuitable. The fluids have an excellent resistance to thermal degradation and may be employed in the formulation of aircraft gas turbine lubricants and heat transfer media expected to undergo severeconditions, including coolants and moderators for nuclear reactants. The lubricating compositions according to the invention may be made by incorporating the radiation resistant fluids in mineral-"oil, especially-in mineral lubricating oil, for use under conditions of radiation exposure and to provide for an increased range of viscosity. In general, the radiation resistant, fluids are added to the petroleum oil in amounts of from about 5% to about 75%, by weight, the usual amount being from 1 about 20% to about 50%. Illustrative examples of the compositions formulated according to the" present invention are shown in Table I, which presents experimental data indicating the change in viscosity under a given dose of gamma radiation. I

Table II gives corresponding datafor' an oil stabilized with various organic sulfide compounds and shows the advantage of the disulfides over the mono-sulfides or cyclic sulfur compounds. It is seen .that the organic disulfides greatly increase theradiation resistance of the partially hydrogenated terphenyls and of the oil and kerosine compositions containing the partially hydrogenated terphenyls. However,: it will be noted that the degree of effectiveness of the aromatic sulfide depends on the composition in which 'it is used. Thus, diphenyl disulfide does not reduce viscosity increase in an aromatic ring system (compare Fluids 1 and 20, Table I),'but'is very effective when parafinic material is added (see Fluid 22, Table I, and Oil I, Table II), whereas dibe'nzyldisulfide is elfective in both types of material, but to a lesser extent than diphenyl disulfide in a predominantly paraffinic system. Metal deactivators may be added to the fluids containing the disulfides and selenides should it be desired to reduce their activity towards metals, such as copper.

TABLE IV.-CATALYTIC OXIDATION TEST [260 F., 40 hours, 10 liters of air per hour, 25 ml. of fluid with Cu, Fe A1 and Pb catalysts] The percentages indicated for the components of the various compositions in Tables I and II are by weight, N.V. Percent based on the total composition. iiiii niiii ni i eia'se sludge Tables III and IV show the advantageous wear and IQ- t 210 oxidation stability of several typical compositions of the invention, l jluigs 0.05 Nil 3 Nil Table V shows the excellent thermal stability of some 8 3; ma mum to 0 05 7 16 N11 0f the compositions listed in Table I in comparison with Flind 7 05 8 4 r ce I O1l13+3% Dlbenzyl a typical aromatic heat transfer 011. disumde (fo Comparison Although the invention has been described herein by with Fluid 05 7 3 e vy means of specific examples and illustrative embodiments thereof, the invention s not to be limited 1n any way 1 Neutralization Vahm thereby but only as indicated in the appended claims.

TABLE I Fluid 'y-Dosage (rods) (in the prezsg ncoe ff small amounts of air at Percent Viscosity Increase- Percent Viscosity Increase- At 100 F. At 210 F. at 100 F. at 210 F.

Mixed partially hydrogenated terphenyls 33 11 70 10% Diphenyl in Fluid 1 9. 5 58 21 20% Diphenyl in Fluid 1.... 19 8. 6 20 20% o-Terphyenyl in Fluid 1 24 10 65 l 27 3% Didodecyl selenide in Fluid 1.- 23 42 19 3% Didodecyl selenide in Fluid 3.. 15 9 28 12 3% Dibenzyl disulfide in Fluid 1 26 1 11 54 l 24 20% Polystyrene (22,000 M.W.) in Fluid 1 (Viscosity at 40 13 84 24 100 F. of 1,200 cs. 90 V.I.). 10% Polystyrene (22,000 M.W.) in Fluid 1 (Viscosity at 5 --5 29 2. 2

100 F. of 250 cs. 83 V.I.). 20% Polystyrene (35,000 M.W.) in Fluid 1 (Viscosity at -15 21 18 -11 100 F. of 3,200 es. 100 V.I.). 10% Polystyrene (35,000 M.W.) in Fluid 1 (Viscosity at -11 -17 3. 8 -15 100,F. of 370 cs. 97 V.I.). 30% Poly-alpha-methylstyrene (boiling range 150300 0. 26 8.9 85 34 at 5mm. Hg) in Fluid 1 (Viscosity at 100 F. of 105 cs.). High \g l. paratfinic light neutral turbine stock 32 cs. at 106 64 400 194 20% Fluid 1 in Oil 13 70 41 266 130 Fluid 1 in Oil 13. 52 30 152 76 20% Fluid 1+3% Dido 1 13 50 29 157 85 50% Fluid 1+3% Didodecyl selenide in Oil 13. 38 21 97 52 Low sulfur kerosine (1.4 cs. at 100 F. 205 40% Fluid 1+10% Diphenyl in kerosine 18 30 100 Fluid 1+ 3% Diphenyl disulfide (for comparison With 7). 35. 3 13. 0 72 27 Fluid 1+3% Diphenyl mono-sulfide (for comparison with 27 Fluid 15+ 3% Dlphenyl disulfide 45. 6 22. 3 93. 0 41. Z

1 Approximate.

TABLE II -Dosage (rads) (in presence of small amounts of air at 20 C.) Percent Vis- Percent Vis- Percent Vis- Percent Viscosity cosity cosity cosity Increase at Increase at Increase at Increase at 100 F. 210 F. 100 F. 210 F.

011 13 (for comparison) 106 64 400 194 13+3% Diphenyl disulfide 62 38 137 78 13+3% Diphenyl mono-sulfide 83 51 257 142 13+10% Thionaphthene 100 55 288 141 13+3% Dibenzyl disulfide 59 36 221 107 1 Approximate.

TABLE V.THERMAL STABILITY I [In stainless steel bombs under nitrogen at 650 F.] TABLE III.WEAR TEST [Shell 4-ball machine; wear scar diameter (cm.) after 10 minutes] Average Ga Evolution Rate, Percent Viscosity Fluid Soar Diameter m1. gas/gm. Fluid/Day (at N.T.P.) from 70240 Hours At 45 kg. Load At 100 kg. Load Aromatic Heat Transfer Oil (initial boiling point 000 F.) for Comparison What is claimed is:

1. A radiation resistant composition comprising a liquid petroleum hydrocarbon and from about 5% to about 75 by weight, of a partially hydrogenated terphenyl.

2. The composition of claim 1 wherein the hydrocarbon is a mineral lubricating oil.

3. A composition according to claim 1 wherein the hydrocarbon is kerosene.

4. A method of lubricating the metal surfaces of equipment wherein the lubricating oil is exposed to radiation comprising the step of applying to the said metal surfaces a lubricant consisting essentially of from about 25% to about 95% by weight of a mineral oil normally prone to radiation deterioration and from about 75% to about 5% by Weight of a partially hydrogenated terphenyl.

5. The method of claim 4 wherein there is additionally present a minor amount of didodecyl selenide.

References Cited UNITED STATES PATENTS FOREIGN PATENTS 2/ 1959 Great Britain. 4/1962 Great Britain. 12/ 1962 Great Britain. 2/ 1963 Great Britain.

' DANIEL E. WYMAN, Primary Examiner.

L. G. XIARHOS, Assistant Examiner. 

4. A METHOD OF LUBRICATING THE METAL SURFACES OF EQUIPMENT WHEREIN THE LUBRICATING OIL IS EXPOSED TO RADIATION COMPRISING THE STEP OF APPLYING TO THE SAID METAL SURFACES A LUBRICANT CONSISTING ESSENTIALLY OF FROM ABOUT 25% TO ABOUT 95% BY WEIGHT OF A MINERAL OIL NORMALLY PRONE TO RADIATION DETERIORATION AND FROM ABOUT 75% TO ABOUT 5% BY WEIGHT OF A PARTIALLY HYDROGENATED TERPHENYL.
 5. THE METHOD OF CLAIM 4 WHEREIN THERE IS ADDITIONALLY PRESENT A MINOR AMOUNT OF DIDODECYL SELENIDE. 